1. Field of the Invention
The present invention generally relates to methods and systems for providing illumination of a specimen for inspection. Certain embodiments relate to methods and systems for providing illumination of a specimen for inspection using an electrodeless lamp.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a large number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield in the manufacturing process and thus higher profits. When inspecting specular or quasi-specular surfaces such as semiconductor wafers, bright field (BF) and dark field (DF) modalities are used. In BF inspection systems, collection optics are positioned such that the collection optics capture a substantial portion of the light specularly reflected by the surface under inspection. In contrast, in DF inspection systems, the collection optics are positioned out of the path of the specularly reflected light such that the collection optics capture light scattered by objects on the surface being inspected such as microcircuit patterns or contaminants on the surfaces of wafers.
Many different light sources have been used in inspection systems. For example, electrode based, relatively high intensity discharge arc lamps are used in inspection systems. However, these light sources have a number of disadvantages. For instance, electrode based, relatively high intensity discharge arc lamps have brightness limits and power limits due to electrostatic constraints on current density from the electrodes, the limited emissivity of gases as black body emitters, the relatively rapid erosion of electrodes made from refractory materials due to the presence of relatively large current densities at the cathodes, and the inability to control dopants (which can lower the operating temperature of the refractory cathodes) for relatively long periods of time at the required emission current.
Light emitting plasmas that are pumped by infrared lasers have been developed for various applications. For instance, some carbon dioxide laser produced plasmas have been produced and studied though not disclosed for use as imaging light sources or in wafer or reticle inspection applications. Examples of such plasmas are described in: Smith, Appl. Phys. Lett., 19(10), 405-408 (1971), S. Jeng and D. Keefer, Journal of Applied Physics, (7), 2272-2279, (1986), G. I. Kozlov, V. A. Kuznetsov, and V. A. Masyukov, Soviet Physics JETP, (39), 463-, (1974), which are incorporated by reference as if fully set forth herein.
Accordingly, it may be advantageous to develop electrodeless light sources for inspection applications, for example, by optimizing the operation of deep ultraviolet (DUV) electrodeless lamps for use as sources in applications for inspection such as semiconductor wafer inspection, and such optimization may include optimizing the pressure, gas type, energy deposition, and energy deposition profile of the lamp while at the same time eliminating the need for electrodes.